The present invention relates to a plasma processing apparatus for performing plasma processing such as etching, ashing, or CVD processing for a substrate such as a semiconductor wafer or an LCD substrate.
As an apparatus for performing plasma processing such as etching for a substrate such as a semiconductor wafer or an LCD substrate, various plasma processing apparatuses including a parallel plate plasma processing apparatus, an ECR (Electron Cyclotron Resonance) plasma processing apparatus, and an inductive coupled plasma processing apparatus have conventionally been known.
The parallel plate plasma processing apparatus will be exemplified. The parallel plate plasma processing apparatus comprises a processing chamber arranged in an airtight processing vessel, upper and lower electrodes arranged opposite to each other within the processing chamber, and a power supply for applying an RF power having a predetermined frequency to either one of the upper and lower electrodes. A predetermined processing gas introduced into the processing chamber is converted into a plasma by the RF power to perform predetermined plasma processing for a substrate with this plasma.
In this plasma processing apparatus, when the RF power having a predetermined frequency is continuously applied to either one of the upper and lower electrodes, the electron temperature in the processing chamber increases to excessively progress dissociation of the processing gas. As a result, the selectivity and the etching rate in a hole undesirably decrease. In the conventional processing apparatus, increases in selectivity and etching rate in the hole are limited. To cope with the increase in integration degree and size reduction of recent semiconductor devices, demand arises for a technique capable of micropatterning (e.g., hole processing with a high aspect ratio). To meet this demand, the above limitations must be overcome.
An improved apparatus forms an RF pulse train (pulse train formed by ON/OFF-controlling or high-level/low-level-controlling an RF signal, and each pulse in the pulse train including an RF component). This RF pulse train is amplified to form an RF power pulse train, which is applied to either one of the upper and lower electrodes to form a pulse plasma (plasma formed intermittently).
This apparatus can form an intermittent pulse plasma in the processing chamber, suppress an increase in electron temperature within the processing chamber, and dissociate a processing gas at an arbitrary rate. Therefore, the selectivity and the etching rate in the hole can be increased.
While no RF power is supplied, no plasma exists between the upper and lower electrodes. While the RF power is at low level, or after glow discharge occurs, the plasma density between the upper and lower electrodes is low. During these periods, since the capacitance between the upper and lower electrodes is smaller than that in occurrence of a plasma, the resonance conditions differ from those in occurrence of a plasma. For this reason, the resonance conditions are not matched in the conventional apparatus wherein the RF power pulse train having a predetermined frequency is applied to the upper or lower electrode. The plasma generation efficiency decreases during the above periods, resulting in a low plasma processing rate.
Immediately after each pulse of the RF power pulse train rises, or during the OFF period, the impedance between the upper and lower electrodes abruptly changes. A conventional matching circuit cannot follow this abrupt change in impedance, and a reflected wave generated upon application of the RF power to the electrode is difficult to relax.
In the conventional apparatus, during a period immediately after each pulse of the RF power pulse train rises, the electron temperature may abruptly increase to damage the substrate.
A plasma processing apparatus wherein a pulse plasma is uniformly drawn into a substrate by applying a biasing RF power pulse train to a lower electrode mounting the substrate thereon is proposed. In this plasma processing apparatus, when each pulse of a plasma generation RF power pulse train rises or is in the OFF state, the maximum and minimum voltage values (V.sub.PP) of the RF power applied to the substrate, or the average voltage value (V.sub.DC) of the RF power applied to the substrate abruptly changes to damage the substrate such that a gate oxide film of a semiconductor wafer is destructed.